Manifold imaging process

ABSTRACT

A MANIFOLD IMAGING SYSTEM WHEREIN A COHESIVELY WEAK PHOTORESPONSIVE IMAGING LAYER IS SANDWICHED BETWEEN TWO SHEETS. THE IMAGING LAYER IS EXPOSED TO A PATTERN OF ACTINIC ELECTROMAGNETIC RADIATION AND AN ELECTRIC FIELD PROVIDING UPON SEPARATION OF THE SHEETS A POSITIVE IMAGE ON ONE SHEET AND A NEGATIVE IMAGE ON THE OTHER.

Dec. 26, 1972 w. 5. VAN DORN MANIFOLD IMAGING PROCESS Filed Feb. 26, 1968 MT Xi U 4 4. 4 N /u /H...\ {K

FIG.2

FIG! ACTIVATE SANDWICH APPLY FIELD AND EXPOSE SEPARATE INVENTOR. WARREN G. VAN DORN ATTORNEYS United States Patent US. Cl. 96-1 R 16 Claims ABSTRACT OF THE DISCLOSURE A manifold imaging system wherein a cohesively weak photoresponsive imaging layer is sandwiched between two sheets. The imaging layer is exposed to a pattern of actinic electromagnetic radiation and an electric field providing upon separation of the sheets a positive image on one sheet and a negative image on the other.

BACKGROUND OF THE INVENTION The present invention relates in general to imaging and, more specifically, to a new system for the formation of very high gamma images by layer transfer in image configuration. This application is a continuation-in-part of copending application, Ser. No. 452,641, filed May 3, 1965, now abandoned.

Although imaging techniques based on layer transfer of a colored material have been known in the past, these techniques have always been clumsy and difficult to operate because they depend upon photochemical reactions and generally involve the use of distinct layer materials for the two functions of imagewise transfer and image coloration. A typical example of the complex structures and sensitive materials employed in prior art techniques is described in US. Pat. 3,091,529 to Buskes. Not only does this type of prior art imaging system tend toward complexity in structure in that it employs separate materials for final image coloration and imagewise transfer but, in addition, imagewise transfer generally depends upon a photo-induced chemical reaction which changes the adhernce of the layer so exposed. The effectiveness of this type of photochemical reaction depends, in turn, upon the vagaries of catalysts used in this system, temperature, pH and many other factors which influence the speed and effectiveness of chemical reactions in general. Many of the prior art systems employ light-sensitive diazo compounds which are, of course, notoriously slow in their response to light. In addition, because of the complexities and critical nature of prior art systems, they are for the most part, diflicult and expensive to prepare in the first instance and then can only be used by trained operators.

SUMMARY OF THE INVENTION It is accordingly an object of this invention to provide a new high gamma photographic system.

It is a further object of this invention to provide a high contrast photographic strip-out process.

The above objects and others are accomplished in accordance with this invention by an imaging system utilizing a structure comprising an electrically photosensitive cohesively weak imaging layer sandwiched between a donor sheet and a receiving sheet. An electric field is imposed across the imaging layer and the imaging layer is exposed to imagewise actinic electromagnetic radiation. Upon separation of the donor and receiver sheets the imaging layer fractures in imagewise configuration corresponding to the imagewise exposure with a positive image adhering to one of the sheets and a negative image Patented Dec. 26, 1972 adhering to the other sheet. Although imaging layers may be prepared which are themselves sufficiently cohesively weak to respond to application of light and field, a larger range of materials may be used if an activating step is included in the process. The activating step serves to weaken the imaging layer so that it can be more easily fractured along a sharp line which defines the image to be reproduced. Conventionally, the imaging layer is activated by treating it with a swelling agent or partial solvent for the material prior to placing the imaging layer between the donor and receiver sheets. The activating step could be omitted if, for example, the layer retains sufficient residual solvent after having been coated on a substrate from a solution or paste to render the layer cohesively weak.

The structure of the manifold set may take many forms. For example, the manifold set may include separate electrodes on opposite sides of the donor substrate and receiver sheet for the application of the field or they may be directly on the back surfaces of these members and in tegral therewith. In another field application technique, one or both of the donor substrate and receiver sheet may be made of a conductive material. Conventionally, at least one of these is transparent so as to permit exposure of the imaging layer through this electrode. Where both separate electrodes and a receiving and/or donor sheet are used, the receiving sheet and receiving side electrode or the donor sheet and donor side electrode may be transparent to permit exposure of the imaging layer. The imaging layer may be exposed from either the receiving sheet side or the donor sheet side.

Although the imaging layers may be prepared as selfsupporting films, normally, these layers are quite thin and for ease of manufacture and handling are coated onto a sheet referred to as the donor sheet or substrate. For convenience the combination of imaging layer and donor sheet is referred to as the donor. The imaging layer of this invention serves the dual function of imparting light sensitivity to the system while at the same time acting as the colorant for the final image produced, although other colorants such as dyes and pigments may be added to it so as to intensify or modify the color of the final images produced when image color is important. The imaging layer may be homogeneous; however, in a preferred form of the invention which has produced superior results a material such as a pigment is dispersed in an insulating binder which is or may be rendered cohesively weak. The use of an insulating binder is preferred because it allows the use of a larger range of electrically photosensitive materials.

In a particularly preferred form of the invention an imaging layer comprising a photosensitive pigment dispersed in an insulating binder is coated onto a transparent, insulating donor sheet. The donor is placed imaging layer side up on a transparent conductive electrode. The imagin g layer is then activated by spraying or brushing a swelling agent or partial solvent for the imaging layer onto the surface of the imaging layer. An insulating receiver sheet is placed on the activated imaging layer. An electrode is then placed on the receiving sheet. A field is then applied between the electrodes and a light image is projected through the donor side electrode and donor sheet. The electrodes are then removed and the receiver sheet and donor sheet are separated providing a positive image corresponding to the light image on one of the donor and receiver sheets and a negative image on the other other sheet.

Whether the positive image is formed on the donor sheet or the receiver sheet depends on the imaging layer materials used and the polarity of the applied field. It has been found in general, however, that if exposure is made through the donor sheet as described above and if the donor side electrode is held at a negative potential in respect to the receiver side electrode, that the positive image is formed on the donor sheet and a negative image is formed on the receiving sheet. That is, the illuminated portions of the imaging layer adhere to the receiving sheet and the non-illuminated areas of the imaging layer adhere to the donor sheet.

It has also been found in general that when the imaging layer is initially coated onto a donor sheet, the best quality images are produced by exposing through the donor sheet. Further, it has been found that the best quality images are formed when the electrode through which exposure is made is maintained at a negative polarity in respect to the non-illuminated electrode.

The strength of the electrical field applied across the manifold set depends on the structure of the manifold set and the materials used. For example, if highly insulating receiver and donor sheet materials are used, a much higher field may be applied than if relatively conductive donor and receiver sheets are used. The field strength required may, however, be easily determined. If too large a potential is applied, electrical breakdown of the manifold set will occur allowing arcing across the manifold set. If too little potential is applied, the imaging layer will not fracture in imagewise configuration. By way of example, if a 3 mil Mylar (a polyester formed by the condensation reaction between ethylene glycol and terephthalic acid available from the E. I. du Pont de Nemours & Co., Inc.) receiver sheet and a 2 mil Mylar donor sheet are used, potentials as high as 20,000 volts may be applied between the electrodes. The preferred field strengths across the manifold set are, however, in the range of from about 1,000 volts per mil to about 4,000 volts per mil. Since relatively high potentials are utilized, it is desirable to insert a resistor in the circuit to limit the flow of current. Resistors on the order of from about 1 megohm to about 20,000 megohms are conventionally used.

A visible light source, an ultraviolet light source or any other suitable source of actinic electromagnetic radiation may be used to expose the imaging layer of this invention. The electrically photosensitive material is chosen so as to be responsive to the wavelength of the electromagnetic radiation used. It is to be noted that diflerent photoresponsive materials have different spectral responses and that the spectral response of many photoresponsive materials may be modified by dye sensitization so as to either increase and narrow the spectral response of a material to a peak or to broaden it to make it more panchromatic in its response. Thus, the material can be used to make ordinary black and white images using panchromatic response while narrow spectral response materials may be employed for the production of color separations or the like. In addition, manifold images formed on transparent materials using different colored imaging layers such as cyan, magenta and yellow may be combined to produce full natural color images by supra position. Also, either the receiver or donor sheet may be opaque providing a print on one or the other sheet.

The manifold sets may be supplied in any color desired either by taking advantage of the natural color of the photoresponsive or binder materials in the imaging layer of the manifold set or by the use of additional dyes and pigments therein whether photeresponsive or not and, of course, various combinations of these photoresponsive and non-photoresponsive colorants may be used in the imaging layer so as to produce the desired color.

The main characterizing property of the system is that it is essentially a go or no go system, so that the imaging layer either adheres to the donor substrate or transfers to the receiver sheet. In those instances where topography or surface configuration of the image is most important, e.g., manufacture of printing plates or resist patterns for printed circuits, the difference between the maximum density of the imaging layer and the substrate or receiver sheet upon which it is supported after imaging may be very small allowing the use of a relatively transparent imaging layer. However, where there is any difference at all between these densities, the system may be defined as a high gamma system, that is, one in which the slope of the density vs. log of exposure curve is very large in that portion of the curve where the imaging layer responds.

The basic physical property desired in the imaging layer is that it be frangible as prepared or after having been suitably activated. That is, the layer must be sufliciently weak structurally so that the application of field combined with the action of actinic radiation on the electrically photosensitive materials will fracture the imaging layer. Further, the layer must respond to the application of field the strength of which is below that field strength which will cause electrical breakdown or arcing across the imaging layer. Another term for cohesively weak, therefore, would be field fracturable.

The imaging layer serves as the photoresponsive element of the system as well as the colorant for the final image produced. Preferably, the imaging layer is selected so as to have a high level of response while at the same time being intensely colored so that a high contrast image can be formed by the high gamma system of this invention. The imaging layer may be homogeneous comprising, for example, a single electrically photosensitive material or may be a solid solution of two or more components with one or more components being electrically photosensitive. The imaging layer may also be heterogeneous comprising, for example, photosensitive pigment particles dispersed in a binder.

One technique for achieving low cohesive strength in the imaging layer is to employ relatively weak, low molecular weight materials therein. Thus, for example, in a single component homogeneous imaging layer, a mono meric compound or a low molecular weight polymer complexed with a Lewis acid to impart a high level of photoresponse to the layer may be employed. Similarly, when a homogeneous layer utilizing two or more components in solid solution is selected to make up the imaging layer, either one or both of the components of the solid solution may be a low molecular weight material so that the layer has the desired low level of cohesive strength. This approach may also be taken in connection with the heterogeneous imaging layer. Although the binder material in the heterogenenous system may in itself be photoresponsive, it does not necessarily have this property so that materials may be seleced for use as this binder material solely on the basis of physical properties and the fact that they are insulating materials without regard to their photoresponse. This is also true of the two-component homogeneous system where nonphotoresponsive materials with the desired physical properties can be used. Any other technique for achieving low cohesive strength in the imaging layer may also be employed. For example, suitable blends of incompatible materials such a blend of a polysiloxane resin with a polyacrylic ester resin may be used either as the binder layer in a heterogeneous system or in conjunction with a homogeneous system in which the photoresponsive material may be either one of the incompatible compone'nts (complexed with a Lewis acid) or a separate and additional component of the layer. The thickness of the imaging layer preferably ranges from about 0.2 micron to about 10 microns.

The imaging layer may contain any suitable electrically photosensitive material. Typical organic materials include; quinacridones such as:

2,9-dimethyl quinacridone,

4,l l-dimethyl quinacridone, 2,10-dichloro-6,l3-dihydro-quinacridone, 2,9-dimethoxy-6,13-dihydro-quinacridone, 2,4,9, 1 1-tetrachloroquinacridone,

6-hydroxy-2,3-di (p-methoxyphenyl) -benzofurane;

2,3 ,5 ,G-tetrap-methoxy-phenyl -furo- 3,2f -benzo- 'furane;

4-dimethylamino-benzylidene-benzhydrazide;

4-dimethyl-aminobenzylideneisonicotinic acid hydrazide;

turfurylidene- (2 -4'-dimethylamino-benzhydrazide;

-benzylidene-amino-acenaphthene-3-benzylideneaminocarbazole;

(4-N,N-dimethylamino-benzylidene -p-N,N-dimethylaminoaniline;

(2-nitro-benzylidene -pbromo-aniline;

N,N-dimethyl-N'- 2-nitro-4-cyano-benzylidene) -pphenylene-diamine;

2,4-diphenyl-quinazoline;

2-(4'-amino-phenyl -4-phenyl-quinaz0line;

2-phenyl-4- (4'-di-methyl-aminophenyl) -7-methoxyquinazoline;

1,3-diphenyl-tetra-hydroimidazole;

1,3-di- (4'-chlorophenyl -tetrahydroimidazole;

1,3-diphenyl-2- (4'- limethylaminophenyl -tetrahydroimidazole;

1,3-di- (p-tolyl -2- [quinolyl- (2'-) ]-tetrahydroimidazole;

3- (4-dimethylamino-phenyl (-5- 4"-methoxy-phenyl) -6- phenyl-1,2,4-triazine;

3-pyridil- (4 -5- (4'-dimethylarninophenyl -6-phenyl 1,2,4-triazine;

3-(4'-amino-phenyl -5,6-diphenyl-1,2,4-triazine;

2,5-bis [4-amino-phenyll l ,3 ,3-triazole;

2,5 -bis [4- N-ethyl-N-acetyl-amino -phenyl- 1' l ,3,4-

triazole;

l,5-diphenyl-3-methyl-pyrazoline;

1,3,4,S-tetraphenyl-pyrazoline;

1-phenyl-3- (p-methoxy styryl -5- p-methoxyphenyl) pyrazoline;

1-methyl-2- 3,4'-dihydroxy-methylene-phenyl) -benzimidazole;

2- (4'-dimethylamine phenyl) -benzoxazole;

2- (4-methoxyphenyl -benzthiazole;

2,5-bis [p-arnino-phenyl-( l 1,3,4-oxidiazole;

4,5 -diphenyl-imidazolone;

3-amino-carbazotle;

copolymers and mixtures thereof.

Other materials include organic donor-acceptor (Lewis acid-Lewis base) charge-transfer complexes made up of aromatic donor resins such as phenolaldehyde resins, phenoxides, epoxies, polycarbonate, urethanes, styrene or the like complexed with electron acceptors such as 2,4,7- trinitro-9-fluoroenone; 2,4,5,7-tetranitro 9 fiuoroenone; picric acid; 1,3,5-trinitro benzene; chloranil; 2,5-dichlorobenzoquinone; anthraquinone-Z-carboxylic acid, 4-nitrophenol; maleic anhydride; metal halides of the metals and metalloids of Groups I-B and II-VIII of the Periodic Table including for example, aluminum chloride, zinc chloride, ferric chloride, magnesium chloride, calcium iodide, strontium bromide, chromic bromide, arsenic triiodide, magnesium bromide, stannous chloride etc.; boron halides, such as boron tri-fiuorides; ketones such as benzophenone and anisil, mineral acids such as sulfuric acid; organic carboxylic acids such as acetic acid and maleic acid, succinic acid, citroconic acid, sulphonic acid, such as 4-toluene sulphonic acid and mixtures thereof. In addition to the charge transfer complexes, it is to be noted that many other of the above materials may be further sensitized by the charge transfer complexing technique and that many of these materials may be dye-sensitized to narrow, broaden or heighten their spectral response curves.

It is also to be understood in connection with the heterogeneous system, that the photoconductive particles themselves may consist of any suitable one or more of the aforementioned photoconductors, either organic or inorganic, dispersed in, in solid solution in, or copolymerized with, any suitable insulating resin whether or not the resin itself s p otqc nduqt ve- This pa ticular typ of particle may be particularly desirable to facilitate dispersion of the particle, to prevent undesirable reactions between the binder 14 and the photoconductor or between the photoconductor and the activator and for similar purposes. Typical resins of this type include polyethylene, polypropylene, polyamides, polymethacrylates, polyacry-lates, polyvinyl chlorides, polyvinyl acetates, polystyrene, polysiloxanes, chlorinated rubbers, polyacrylonitrile, epoxies, phenolics, hydrocarbon resins and other natural resins such as rosin derivatives as well as mixtures and copolymers thereof.

The x-form phthalocyanine is preferred because of its excellent photosensitivity and intense coloration.

The ratio of photoconductor to binder by volume in the heterogeneous system may range from about 10 to 1 to about 1 to 10, but it has generally been found that proportions in the range of from about 1 to 4 to about 2 to I produce the best results and, accordingly, this constitutes a preferred range.

The binder material in the heterogeneous imaging layer or the material used in conjunction with the photorespon'sive material in the homogeneous layer, where applicable, may comprise any suitable cohesively weak insulating. material or materials which can be rendered cohesively weak. Typical materials include: microcrystalline waxes such as: Sunoco 1290, Sunoco 5825, Sunoco 985, all available from Sun Oil Co.; Parafiint RG, available from the Moore and Munger Company; paraffin waxes such as: Sunoco 5512, Sunoco 3425, available from Sun Oil Co.; Sohio Parowax, available from Standard Oil of Ohio; waxes made from hydrogenated oils such as: Capitol City 1380 wax, available from Capitol City Products, Columbus Ohio; Caster Wax L-2790, available from Baker Caster Oil Co.; Vitikote L-304, available from Duro Commodities; polyethylenes such as: Eastman Epolene N11, Eastman Epolene C-12, available from Eastman Chemical Products; Polyethylene DYJT, Polyethylene DYLT, Polyethylene DYDT, all available from Union Carbide; Marlex TR 822, Marlex 1478, available from Phillips Petroleum Co.; Epolene C-13, Epolene C-lO, available from Eastman Chemical Products; Polyethylene AC8, Polyethylene AC612, Polyethylene AC324, available from Allied Chemicals; modified styrenes such as: Piccotex 75, Piccotex 100, Piccotex 120, available from Pennsylvania Industrial Chemical; Vinylacetateethylene copolymers such as: Elvax Resin 210, Elvax Resin 310, Elvax Resin 420, available from Dupont; Vistanex MH, Vistanex L-80, available from Enjay Chemical Co.; vinyl chloride-vinyl acetate copolymers such as: Vinylite VYLF, available from Union Carbide; styrene-vinyl toluene copolymers; polypropylenes; and mixtures thereof.

A mixture of microcrystalline and paraflinic waxes is preferred because it is cohesively weak and a good insulator.

Where the imaging layer is not sufliciently cohesively weak to allow fracture at the time of imaging, it is desirable to apply an activator to the layer to render the layer cohesively weak. The activator serves to swell or otherwise weaken and thereby lower the cohesive strength of the imaging layer. Preferably, the activator should have a high resistivity so as to prevent electrical breakdown of the manifold set. Accordingly, it will generally be found to be desirable to purify commercial grades of activators so as to remove impurities which might impart a higher level of conductivity to the activating fluids. This may be accomplished by running the fluids through a clay column or by any other suitable purification technique. Generally speaking, the activator may consist of any suitable solvent having the aforementioned properties and which has the above-described effect on the imaging layer. For purposes of this specification and the appended claims, the term activator shall be understood to include not only materials which are cqnvcntionally thought of a solvents but also those which are thought of as partial solvents, swelling agents or softening agents for the imaging layer.

It is generally preferable that the activator solvents have a relatively low boiling point so that fixing can be accomplished after image formation by solvent evaporation with mild heating at most. 'It is to be understood, however, that the invention is not limited to the use of these relatively volatile activators. In fact, very high boiling point nonvolatile activators including silicone oils such as dimethylpolysiloxanes and very high boiling point long chain aliphatic hydrocarbon oils ordinarily used as transformer oils such as Wemco-C transformer oil, available from Westinghouse Electric Co., have also been successfully utilized in the imaging process. Although these less volatile activators do not dry off by evaporation, image fixing can be accomplished by rolling off the final image pro duced on an absorbent sheet such as paper which soaks up the activator fluid. In short, any suitable volatile or nonvolatile activator may be employed. Typical activators include Sohio Odorless Solvent 3440, an aliphatic (kerosene) hydrocarbon fraction, available from Standard Oil Co. of Ohio, carbon tetrachloride, petroleum ether, Freon 214 (tetrafiuorotetrachloropropane), other halogenated hydrocarbons such as chloroform, methylene chloride, trichloroethylene, perchloroethylene, chlorobenzene, trichloromonofluoromethane, tetrachlorodifluoroethane, trichlorotrifiuoroethane, amides such as formamide, dimethyl formamide, esters such as ethyl acetate, isopropyl acetate, butyl acetate, amyl acetate, cyclohexyl acetate, isobutyl propionate and butyl acetate, ethers such as diethyl ether, diisopropyl ether, dioxane, tetrahydrofuran, ethyleneglycol monoethyl ether, aromatic and aliphatic hydrocarbons such as benzene, toluene, xylene, hexane, cyclohexane, gasoline, mineral spirits and white mineral oil, ketones such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone and vegetable oils such as coconut oil, babussu oil, palm oil, olive oil, castor oil, peanut oil and neatsfoot oil, decane, dodecane, and mixtures thereof. Sohio Odorless Solvent 3440 is preferred because it is an excellent insulator and evaporates readily.

The electrodes may comprise any suitable conductive material and may be flexible or rigid. Typical conductive materials include: metals such as aluminum, brass, steel, copper, nickel, zinc, etc., metallic coatings on plastic substrates, rubber rendered conductive by the inclusion of a suitable material therein, or paper rendered conductive by the inclusion of a suitable material therein or through conditioning in a humid atmosphere to insure the presence therein of sufiicient water content to render the material conductive. Conductive rubber is preferred because of its excellent flexibility.

The transparent conductive electrode may be made of any suitable conductive transparent material and may be I flexible or rigid. Typical conductive transparent materials include cellophane, conductively coated glass, such as tin or indium oxide coated glass, aluminum coated glass, or similar coatings on plastic substrates. NESA, a tin oxide coated glass available from Pittsburgh Plate Glass Co., is preferred because it is a good conductor and is highly transparent.

The donor substrate and receiving sheet may comprise any suitable insulating or conducting material. Insulating materials are preferred since they allow the use of high strength polymeric materials. Typical insulating materials include polyethylene, polypropylene, polyethylene terephthalate, cellulose acetate, paper, plastic coated paper, such as polyethylene coated paper, vinyl chloride-vinylidene chloride copolymers and mixtures thereof. Mylar is preferred because of its durability and excellent insulative properties. Not only does the use of this type of high strength polymer provide a strong substrate for the positive and negative images formed on the donor substrate and receiver sheet but, in addition, it provides an electrical barrier between the electrodes and the imaging layer which tends to inhibit electrical breakdown of the system.

10 BRIEF DESCRIPTION OF THE DRAWINGS The advantages of this improved method of imaging will become apparent upon consideration of the detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a side sectional view of a photosensitive imaging manifold set for use in the invention.

FIG. 2 is a side sectional view of a second photosensitive imaging manifold set.

FIG. 3 is a process flow diagram of the method steps of the invention.

FIGS. 3a and 3b are side sectional views diagrammatically illustrating the process steps of the invention.

Referring now to FIG. 1 of the drawings, there is seen a supporting donor substrate layer 11 and an imaging layer generally designated 12. In the manufacture of the imaging member, herein referred to as the manifold set, layer 12 is preferably coated on substrate 11 so that it adheres thereto. These layers are collectively referred to as the imaging donor or merely the donor. In this particular illustrative example, layer 12 consists of photoconductive pigment 13 dispersed in a binder 14. Above imaging layer 12 is a third or receiving layer .16. This receiver sheet is ordinarily supplied as a separate layer which does not initially adhere to layer 12. Accordingly, al though the whole imaging member or manifold set may be supplied in a convenient three-layer sandwich as shown in FIG. 1, receiving layer 16 may also be supplied as a separate sheet or roll if desired. On the other hand, in those systems where activation of the imaging layer is not required or where imaging layer 12 has been preactivated, layer 16 may adhere to or be tacked onto imaging layer 12. In the particular embodiment of the manifold set shown in FIG. 1, both the donor substrate 11 and the receiver sheet 16 are made up of an electrically conductive material such as cellophane with at least one of them being optically transparent to provide for the exposure of layer 12. In this embodiment of the manifold set layers 1:1 and 16 also act as the electrodes.

Referring now to FIG. 2. which shows the preferred manifold set embodiment, imaging layer 12 is deposited on an insulating donor substrate 17 which is backed with a conductive electrode layer 18. The image receiving portion of the manifold set also consists of an insulating receiver sheet 19 backed with a conductive electrode layer 21. Here again, either or both of the pairs of layers 17- 18 and layers 19-21 may be transparent so as to permit exposure of imaging layer 12. Flexible, transparent conductive materials, such as cellophane which may be used in the FIG. 1 embodiment of the invention, are for the most part relatively weak materials with the choice of these materials being quite limited. The FIG. 2 structure which uses an insulating donor substrate and receiver sheets 17 and 19, respectively, allows for the use of high strength insulating polymeric materials.

Combinations of the structure described in FIGS. 1 and 2 may also be used in carrying out the invention with a relatively conductive layer immediately in contact with one side of imaging layer 12 and a conductively backed insulating layer on the other side of the imaging layer.

Referring now to the flow diagram of FIG. 3, it is seen that when required the first step in the imaging process is the activation step. In this stage of the imaging process, the manifold set is opened and the activator is applied to imaging layer 12 following which these layers are closed back together again, as indicated in the second block of the process flow diagram of FIG. 3. Although the activator may be applied by any suitable technique, such as with a brush, with a smooth or rough surfaced roller, by flow coating, by vapor condensation or the like, FIG. 3a which diagrammatically illustrates the first two process steps shows the activator fluid 23 being sprayed on to imaging layer 12 of the manifold set from a container 24. The activator serves to swell or otherwise weaken and thereby lower the cohesive strength of imag- 11 ing layer 12. The activator should preferably have a high level of resistivity to help prevent electrical breakdown of the manifold set.

It is generally preferable to include an activation step in the imaging process because if this step is included, then a stronger and more permanent imaging layer 12 may be provided which can withstand storage and transportation prior to imaging.

Following the deposition of the activator fluid, the set is closed by a roller 26 which also serves to squeeze out any excess activator fluid which may have been deposited.

Although it is preferred to use a separate electrode, sheet 16 in FIG. 3a and FIG. 3b for simplicity is shown as a conductive receiver sheet which also acts as an electrode.

Potential source 28 is connected to resistor 30 receiver sheet 16 and transparent conductive electrode 18. An electrical field is applied across the manifold set and it is exposed to the image 29 to be reproduced. Upon separation of substrate 17 and receiving sheet 16, imaging layer 12 fractures along the edges of exposed areas. Accordingly, once separation is complete, exposed portions of imaging layer .12 are retained on one of layers 17 and 16 while unexposed portions are retained on the other layer, resulting in the simultaneous formation of a high gamma positive image on one of the sheets and a high gamma negative image on the other.

Although FIG. 3b shows a positive image being formed on the surface of substrate 17 and a negative image on sheet 16, the positions of these images may be reversed depending on the field applied and the photoconductive materials used. Further, although layer 12 is shown as being exposed from the donor side, the layer may also be exposed from the receiver side.

If a relatively volatile activator is employed, such as petroleum ether or carbon tetrachloride, fixing occurs al most instantaneously after separation of layers 17 and 16 because the relatively small quantity of activator in the layer of imaging material flashes off very rapidly. With somewhat less volatile activators, such as the Sohio Odorless Solvent 3440 or Freon 214, described above, fixing may be accelerated by flowing air over the images or warming them to about 150 F., whereas with the even less volatile activators, such as transformer oil, fixing is accomplished by absorption of the activator into another layer such as a paper substrate to which the image is transferred. Many other fixing techniques and methods for protecting the images such as overcoating, laminating with a transparent thermoplastic sheet and the like will occur to those skilled in the art. Increased image durability and hardness may also be achieved by treatment with an image material hardening agent or with a hard polymer solution which will wet the image material.

In general, the apparatus for carrying out the imaging procedure described above will employ the elements illustrated in FIGS. 3a and 3b including a source of activator fluid, a squeegee roller to remove excess activator fluid, a power supply with series resistor and a set of electrodes which may or may not be built in to the manifold set. Opening the manifold set for activator, closing the set for exposure and opening again for separation and image formation may be accomplished by any one of a number of techniques which will be obvious to those skilled in the art. However, one straightforward way to accomplish this reuslt is to supply the imaging materials in the form of long webs which can be entrained over rollers so as to provide opening and closing of the set during the imaging process.

DESCRIPTION OF PREFERRED EMBODIMENTS The following examples further specifically illustrate the present invention. The examples below are intended to illustrate various preferred embodiments of the improved imaging system. The parts and percentages are by 7 Weight unless otherwise indicated.

EXAMPLES I-IV A commercial, metal-free phthalocyanine is first purified by acetone extraction to remove organic impurities. Since this extraction step yields the less sensitive beta crystalline form, the alpha form is obtained by dissolving grams of beta in 600 cc. of sulfuric acid, precipitating it by pouring the solution into 3,000 cc. of ice water and washing with water to neutrality. The thus purified alpha phthalm cyanine is then salt milled for 6 days and desalted by slurry-ing in distilled water, vacuum filtering, water Washing and finally, methanol washing until the initial filtrate is clear. After vacuum drying to remove residual methanol the x-forrn phthalocyanine thus produced is used to prepare the imaging layer according to the following procedure: 5 grams of Sunoco 1290, a microcrystalline wax with a melting point of 178 F. is dissolved in 100 cc. of reagent grade petroleum ether heated to 50 C. and quenched by immersing the container in cold water to form small wax crystals. Five grams of the purified and milled phthalocyanine produced according to the above procedure are then added to the wax paste along with /2 pint of clean porcelain balls in a 1 pint mill jar. This formulation is then ball milled in darkness for 3 /2 hours at 70 r.p.m. and after milling 20 cc. of Sohio Solvent 3440 is added to the paste. This paste is then coated in subdued green light on a 2 mil Mylar sheet with a No. 12 wire-wound draw down rod which produces a 2.5 micron thick coating after drying. The same paste is also applied on three other Mylar sheets with a No. 8 draw down rod to produce a coating thickness of 1 /2 microns, with a No. 24 rod to produce a coating thickness of 5 microns and a No. 36 rod to produce a coating thickness of 7 /2 microns. Each of these coatings is then heated to about F. in darkness in order to dry it. Then the coated donors are placed on the tin oxide surface of NESA glass plates with their coatings facing away from the tin oxide. A receiver sheet also of 2 mil thick Mylar is then placed on the coated surface of each donor. Then a sheet of black, electrically conductive paper is placed over the receiver sheet to form the complete manifold set. The receiver sheet is then lifted up and the phthalocyanine Wax layer is activated with one quick brush stroke of a wide camels hair brush saturated with petroleum ether. The receiver sheet is then lowered back down and a roller is rolled slowly once over the closed manifold set with light pressure to remove excess petroleum ether. The negative terminal of an 8,000 volt DC. power supply is then connected to the NESA coating in series with a 5,500 megohm resistor and the positive terminal is connected to the black opaque electrode and grounded. With the voltage applied, a white incandescent light image is projected upward through the NESA glass using a Wollensak 90 mm., ;f 4.5 enlarger lens with illumination of approximate 1y M foot-candle applied for 5 seconds for a total incident energy of 0.05 foot-candle-second. After exposure, the receiver sheet is peeled from the set with the potential source still connected. The small amount of petroleum ether present evaporates within a second or so after separation of the sheets yielding a pair of excellent quality images with a duplicate of the original on the donor sheet and a reversal of the original on the receiver sheet. All four coating thicknesses produce good quality images; however, it is apparent that there is a slight increase in sensitivity and gamma with increasing thickness of the phthalocyanine wax coating.

EXAMPLES V-VIII Five donor substrates are coated according to the procedure of Example I except that the ratio of phthalocyamne pigment to wax is 5 to 1 in Example V, 1 to 4 in Example VI, 1 to 5 in Example VII and 1 to 10 in Example VIII. When these donors are imaged according to the procedure of Example I, all produce dense high resolution images with the exception of Example VIII which produces a coating of lower reflection density and noticeably lower resolution.

PLES IX-XIII The procedure of Example I is repeated except that the phthalocyanine pigment is mixed at a ratio of l to 1 for each of the following binders: for Example IX Sunoco microcrystalline wax grade 5 825 having an ASTM-D-127 melting point of 151 F. is used; for Example X, grade 985, another Sunoco microcrystalline wax having a melting point of 193 F. is used; for Example XI, Sunoco paraffin wax grade 5512 having a melting point of 153 F. (ASTMD-87) is used; for Example XII, a low molecular weight polyethylene sold by Eastman Chemical Products, Inc. under the tradename Epolene C-12 having an approximate molecular weight of 3,700, a ring and ball softening point of 92 C., an acid No. of 0.05 and a density at 25 C. of 0.893 is used; for Example XIII, grade N-11 of the Epolene low molecular weight polyethylene series is employed having an approximate molecular weight of 1,500, a ring and ball softening point of 170 C., a density at 25 C. of .924 and an acid number of metal-free phthalocyanine is used. This is produced by the same acetone extraction and precipitation from sulfuric acid solution with no milling. In Example XXI, Algol Yellow GC Color Index No. 67,300 (1,2,5,6-di (C,C'-diphenyl)thiazole-anthraquinone is used. In Example XXII, the pigment used is 2,9-dirnethylquinacridone. In Example XXIII, French process zinc oxide is used as the pigment. In Example XXIV, mercuric sulfide is used as the pigment. While all of these materials produce images, it is found that the stabilized alpha phthalocyanine of Example XIX has about one order lower sensitivity as the X-crystal form of Example I while the beta phthalocyanine is about two orders of magnitude slower than this speed. Contrasting the remaining pigments, it is found that 750 foot-candle-seconds exposure is required in EX- ample XXI, 10,500 foot-candle)seconds is required in Example XXII, 5,000 foot-candle-seconds is required in Example XXIII and 10,000 foot-candle-seconds in Example XXIV.

EXAMPLES XXV-XXVIII Four imaging members or manifold sets are made up and imaged according to the procedure of Example I with the exception that various electrodes, donor subof 0.05. Each of these coatings is imaged according to strates and receivers are employed as follows:

Example Base electrode Donor substrate Receiver sheet Upper electrode XXV Cellophane Electrode Electrode Cellophane. XXVI .do Mylar "do Do. XXVII N ESA glms Cellulose acetate Cellulose acetate Conductive black paper. XXVIII do Mylar Electrode Aluminum.

the procedure of Example I and all are found to produce good quality images, although Sunoco 5 825 microcrystalline wax of Example IX and 5512 parafiin wax of Example XI produce some blue ha'ze in the background of the image which remains on the donor apparently because of the fact that these waxes are softer than the other materials tested.

EXAMPLES XIV-XVIII Five donors are prepared according to the procedure of Example I and imaged according to the procedure given in that example with the exception that the following activators are used in each of the examples. In Example XIV, it is activated with Sohio Odorless Solvent 3440; Example XV is activated with carbon tetrachlorides; Example XVI is activated with Freon 214 (tetrachlorotetrafluoropropane); Example XVII is activated with Dow- Corning silicone oil DC200 (dimethylpolysiloxane), and Example XVIII is activated with Wemco-C transformer oil, a very high boiling point long chain aliphatic oil available from Westinghouse Electric. In each of these examples, the activators produce a high quality image upon separation. In the case of Examples XIV-XVI, the final images require mild heating at most to dry 'ofi the activator and harden the image, while in the case of Examples XVII and XVIII, the non-drying activator maintains the image in a wet condition. These two images are then rolled ofi on an absorbent paper substrate which picks up most of the activator thereby hardening the imaging material in the surface.

EXAMPLES XIX-XXIV In Examples XD(XXIV, six donors are made according to the procedure of Example I and the imaging procedure of Example I is followed with the only exception that the pigment used in forming the imaging layer is as follows: in Example XIX, the stabilized alpha crystalline form of metal-free phthalocyanine is employed. This material is prepared by acetone extraction of the commercial metal-free phthalocyanine and sulfuric acid solution reprecipitation of the extracted material as in Example I followed by neat milling for one day of the precipitated material in a porcelain mill with Burundum balls. This milling stabilizes the alpha form from conversion to the beta form. In Example X, the beta form Each of these structures produces results which are about equivalent to those of the Example I procedure.

EXAMPLE XXIX Eight parts by weight of 2,5-bis (p-aminophenyl) 1,3,4 oxidiazole and 12 parts by weight of Lucite 2008, a low molecular weight polymethylmethacrylate available from 'E. I du Pont & Co., are dissolved in '80 parts by weight of methylethyl ketone along with 0.25 part by weight of bromphenol blue dye. This solution is then coated on a 2 mil Mylar substrate and before the coating is fully dried, it is dipped in a water bath which dilutes the solution causing the solids to precipitate out in a weak semiparticulate form in which the individual particles are bonded at their interfaces much like a sintered layer. The donor thus prepared is imaged according to the procedure of Example I with a Mylar receiver sheet beneath an electrically conductive black paper electrode and using a transparent NESA glass electrode beneath the Mylar layer of the donor. Although the dye increases the sensitivity of the layeg somewhat and imparts a pink tinge to it, both the sensitivity of the system and the resolution of the image produced are lower than that of the system of Example I.

EXAMPLE XXX Twenty parts by weight of polyvinylcarbazole is dissolved in parts by weight of toluene along with 2 parts by weight of a 2,4,7-trinitro-9-fluorenone charge transfer complexing agent and 0.05 part by weight of a bromphenol blue sensitizing dye. After partial drying of the coating, it is dipped in acetone which causes precipitation of the solids from solution in the same type of physical structure as described above in connection with Example XXIX. This donor is imaged according to the same procedure as used in connection with Example XXIX and is somewhat more sensitive than the coating of Example XXIX.

Although specific components and proportions have been stated in the above description of preferred embodiments of the invention, other typical materials as listed above if suitable may be used with similar results. In addition, other materials may be used to synergize, enhance or otherwise modify the properties of the imaging layer. For example, various dyes, spectral sensitizers, particles made up of two or more layers, blends of materials, complexes, and electrical sensitizers such as Lewis acids may be added to the several layers.

Other modifications and ramifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of this invention.

What is claimed is:

1. A method of imaging comprising the steps of:

(a) providing an electrically photosensitive imaging layer structurally fracturable in response to (1) an electric field less than the electrical breakdown potential of said layer and (2) exposure to electromagnetic radiation to which said layer is sensitive sandwiched between a donor layer and a receiver layer at least one of said donor and receiver layers being at least partially transparent to electromagnetic radiation to which said imaging layer is sensitive;

:(bl) applying an electrical field across said imaging ayer;

(c) exposing said imaging layer to a pattern of electromagnetic radiation to which said imaging layer is sensitive; and,

(d) separating said receiver layer from said donor layer while under said electrical field whereby said imaging layer fractures in imagewise configuration with a positive image adhering to one of said donor and receiver layer and a negative image adhering to the other of said donor and receiver layer.

2. The method of claim 1 wherein said imaging layer is coated on at least one of said donor layer and said receiver layer.

3. The method of claim 1 wherein said donor layer and said receiver layer are insulating and further including the step of providing donor and receiver side electrodes and applying said electric field between said donor side and said receiver side electrodes.

4. The method of claim 1 wherein said imaging layer comprises a homogeneous solution of electrically photosensitive material in an insulating binder.

5. The method of claim 1 wherein said imaging layer comprises an electrically photosensitive material containing an organic charge-transfer complex.

6. The method of claim 1 wherein said imaging layer comprises an electrically photosensitive material dispersed in a heterogeneous blend of materials which together form a structure fracturable in response to (1) an electric field less than the electrical breakdown potential of said layer and (2) exposure to electromagnetic radiation to which 50 said layer is sensitive.

7. The method of claim 1 wherein said imaging layer comprises metal-free phthalocyanine in a binder.

8. The method of claim 1 wherein said imaging layer comprises electrically photosensitive material in a binder 55 16 selected from the group consisting of microcrystalline wax, paraifin wax, hydrogenated oil wax, polyethylene, polypropylene, vinyl chloride-vinyl acetate copolymers, styrene-vinyl toluene copolymers, vinyl-acetate-ethylene 'copolymers, methyl-styrene-vinyl toluene copolymers and mixtures thereof.

9. The method of claim 1 wherein said donor layer and said receiver layer are insulating and said electric field has a potential of up to 20,000 volts.

10. The method of claim 1 'wherein said electric field has a field strength of about 1,000 volts per mil to about 4,000 volts per mil across said donor layer, said receiver layer and said imaging layer.

11. The method of claim 1 and further including the step of rendering the imaging layer structurally fracturable in response to (1) an electric field less than the electrical breakdown potential of said layer and (2) exposure to electromagnetic radiation to which said layer is sensitive by means of contacting said layer with an activator.

12. The method of claim 1 wherein the electrically photosensitive imaging layer comprises an organic electrically photosensitive material.

13. The method of claim 1 wherein said imaging layer comprises electrically photosensitive particles dispersed in an insulating binder.

14. The method of claim 13 and further including the step of rendering said imaging layer structurally fracturable in response to (1) an electric field less than the electrical breakdown potential of said layer and (2) exposure to electromagnetic radiation to which said layer is sensitive by means of contacting said layer with an activator.

15. The method of claim 13 wherein the electrically photosensitive particles comprise an organic electrically photosensitive material.

16. A method of claim 13 wherein the ratio by volume of electrically photosensitive particles to binder is in the range of from about 1 to 4 to about 2 to 1 respectively.

References Cited UNITED STATES PATENTS 2,940,847 6/ 1960 Kaprelian 96-1 3,316,088 4/1967 Schoffert 96-15 2,949,848 -8/1960 Mott 101-1283 2,954,291 9/1960 Clark 96-1 3,268,331 8/1966 Harper 96-1 3,287,122 11/1966 Hoegl 96-15 3,384,566 5/1968 Clark 204-181 3,397,086 8/1968 Bartfei 117-218 JOHN C. COOPER HI, Primary Examiner U.S. Cl. X.R. 

